1. Field of the Invention
This invention relates to inflatable drag reducers for the purpose of lessening the partial vacuum that exists behind rectangularly shaped cargo carrying vehicles The addition of such an appendage brings the vehicle closer to the aerodynamically optimal tear drop shape thus significantly reducing aerodynamic drag and fuel consumption. Inflatable rear end drag reducers are superior to rigid versions proposed elsewhere in that they are light, inexpensive and easily collapsible without need of hinges or other moving parts.
2. Prior Art
Labbe(1990) U.S. Pat. No. 4,978,162 shows an automatically inflating drag reducer like the present invention. Labbehowever, has no means for preventing the drag reducer from falling and/or being blown laterally by cross winds thus obstructing rear signal lights when the pressure inside the drag reducer is insufficient to sustain its inflated shape at slow speeds and stops. The elastic recoil means of the present invention not only prevents tail light obstruction but it allows the drag reducer to be larger and more aerodynamically effectively shaped without having the drag reducer fall on the road let alone obstruct tail lights at slow speeds.
Labbe(1990) air tightly fixes the drag reducer along the periphery of the rear face of the vehicle. Hence the rear face of the vehicle serves as the base of the substantially air tight chamber which is created. One difficulty with attempting to air tightly fix the periphery of the drag reducer to the truck doors is that the doors often have irregularities in their surface due to hinge mounting plates, structural supporting rods and the locking system. In the present invention a fully enclosed bag with flexible base is used to create the required pressurized chamber. This arrangement allows the base of the drag reducer to be mounted easily on the truck with no air sealing requirements (see Labbecol 4, line 18). It also allows for an easily detached mounting means for trucks with upward sliding back doors. The drag reducers, which in these cases must be mounted to the frame of the truck, can easily be removed for access to the door.
Kerian (1986) U.S. Pat. No. 4,601,508 also shows an inflated drag reducer with air being ducted to an open plenum. He mentions in col 4, line 39 that a series of internal bungee cords could be installed for urging the outermost edge of the appendage inwardly toward the doors. It is recognized in the present invention that the most parsimonious manner in which to utilize elastic cords without need for many cords or excessive dimpling of the drag reducer surface when inflated, is for the elastic cord(s) to follow the contour of the drag reducer's surface, preferably circumferentially. Such an arrangement allows the surface tension of the drag reducer to efficiently impart force to and thereby extend the elastic cord(s) so that upon deflation effective recoil is achieved.